Hard disk drives are used in many computer system operations. In fact, many computing systems operate with some type of hard disk drive to store the most basic computing information, e.g., the boot operation, the operating system, the applications, etc. In general, the hard disk drive is a device, which may or may not be removable, but without which, some computing systems may not operate.
One basic hard disk drive model was developed approximately 40 years ago and in some ways resembles a phonograph type apparatus. For instance, the hard drive model includes a storage disk or hard disk that spins at a standard rotational speed. An actuator arm or slider is utilized to reach out over the disk. The arm has a magnetic read/write transducer or head for reading/writing information to or from a location on the disk. The complete assembly, e.g., the arm and head, is called a head gimbal assembly (HGA). The assembly consisting of the disks, HGAs, spindle, housing, and the other parts internal to the housing is called the Head Disk Assembly, or HDA.
In operation, the hard disk is rotated at a prescribed speed via a spindle motor assembly having a central drive hub. Additionally, there are data holding channels or tracks spaced at known intervals across the disk. Most current embodiments arrange the data holding regions in concentric circular tracks, but other designs, such as spirals or irregular closed or open paths are possible and useful. When a request for a read of a specific portion or track is received, the hard disk aligns the head, via the arm, over the specific track location and the head reads the information from the disk. In the same manner, when a request for a write of a specific portion or track is received, the hard disk aligns the head, via the arm, over the specific track location and the head writes the information to the disk.
Refinement of the disk and the head have provided reductions in the size of the hard disk drive. For example, the original hard disk drive had a disk diameter of 24 inches. Modern hard disk drives are much smaller and include disk diameters of less than 2.5 inches. Small disk drive type apparatus such as micro drives can be smaller still. Refinements also include the use of smaller components and laser and other optical related components within the head portion. Reducing the read/write tolerances of the head portion allows the tracks on the disk to be reduced in size by a corresponding margin. Thus, as modern laser and other electro-optical and other micro recognition technologies are applied to the head, the track size on the disk can be further compressed.
The ever increasing need for data storage has led some disc drive makers to steadily increase the amount of data stored on a drive. Mechanical considerations, radiated audible noise limits, power requirements, and other factors limit the number of discs that can be economically combined in a single drive. Thus, disc drive technology has generally focused on increasing the amount of data stored on each disc surface.
Typically, data tracks are arranged concentrically about a disk's surface or in an analogous arrangement. One method of increasing the amount of data a disk can store is to make each data track narrower, which allows the tracks to be spaced more closely together. This allows a larger number of tracks on each disk surface. But, as tracks become narrower, signals generated in the head caused by media alterations (e.g., from data written to the disk'magnetic, optical, thermal, and/or other media) become more difficult to detect. Thus, the signal to noise ratio can worsen, particularly in the presence of electronic and media-induced signal degradation and noise.
One method to improve the signal to noise ratio, and hence the detection of media alteration (e.g., “writing”), is to position the heads more closely to the media surface. This causes the media alteration-sensing components of the head to be physically closer to the media alterations, thus improving the head sensor'ability to detect the media alterations comprising the written signal. However, care must be taken to avoid unintended contact between the head components and the moving media surface.
Typically, the heads are lightly spring loaded, with the spring tension perpendicular to the media surface plane and directed against the media surface. An air bearing separates the head and media surfaces as follows: As the media moves relative to the head, air is dragged by the disc surface through specifically designed channels in the surface of the head adjacent to the media surface.
The surface of the head and the channels contained therein, collectively referred to as the air-bearing surface (ABS), are designed to generate a regions of increased air pressure in between the ABS and media surface that forces the head away from direct contact with the media surface, in effect causing the head to fly above the media surface. The separation of the head ABS and media surface, commonly called fly height, is a complex phenomenon primarily a function of air density, the spring preload, the relative speed between the head and media surface, and the pattern of channels present on the head air bearing surface adjacent to the media surface.
Persons skilled in the design of disc drive heads recognize that lower fly heights requires physically smaller head sliders, plus tighter tolerances and greater precision on the dimensions of the slider and air bearing components. In addition, lower fly heights (closer head-disc separation) necessitate very tight control of the flatness and cleanliness of the air bearing surface to minimize the variance in fly height (e.g., population standard deviation of the fly height distribution) and reduce the probability of unwanted head-disc contact.
Many of the air bearing surface structural elements are pads, dams, foils, or other elements designed to direct and control air flow, mechanically support and position head components, provide features to support the head while the disc is not spinning hence the head is not flying, and many other functions. These elements typically consist of a structural material, which typically provides the physical size, strength, durability, and other qualities of the air bearing surface element feature. In addition to the structural material, other layers may be situated both above, e.g. towards the surface facing the media, and below, e.g. towards the slider body layer, the structural layers. These other layers provide corrosion resistive, adhesive, protective, electrical, and other qualities necessary to the head functions, e.g. electrical, mechanical, and aerodynamic properties.
Current air bearing surface technology often uses a “lift off” process to depose structural material, as exemplified in FIG. 1. FIG. 1 is an illustrative example of a lift off process material arrangement, and FIG. 2 exemplifies the structure of the resulting exemplary structural feature. The lift-off process is intended to depose a pattern of structural material having sides essentially perpendicular to a substrate (e.g., slider body) and a flat upper surface parallel to the substrate surface, i.e., a rectangular cross section in the view provided by FIG. 1.
The exemplary lift off process denoted in FIG. 1 uses a protective layer 2 deposited over the slider body substrate 1. Typically, the protective layer is composed of at least two discrete layers, usually a layer of silicon followed by a layer of carbon. Further, a patterned resist layer 3, typically photo resist, is deposited over the protective layer 2, covering the regions where the structural material 4 is not wanted, hence the remaining area constitutes the regions where deposition of the structural material is desired. The shape and perimeter features of said remaining area constitute the shape and perimeter features of the resulting structural element. Next, a layer of the structural material 4 used to construct the air bearing element is deposited over both the protective layer 2 and patterned resist layer 3, with an angle of incidence 7. Then the resist 3, along with the structural material 4 applied over it, are removed from the air bearing surface protective layer 2 by a stripping process, leaving the desired pattern of structural material 6 in FIG. 2. In many cases, the thickness of the structural material necessitates vigorous mechanical methods to break up and remove the undesired structural material and resist layer, such as a soda blast. This vigorous stripping process step may damage the protective layer 2, slider body 1, and any other features or components of the air bearing surface.
The structural element 6 typically contains at least one region 9 that was shadowed by resist 3, hence the height dimension is inadequate. The shadowing is a result of the angle of the deposition flux orientation resulting in regions where the structural material deposition flux is reduced, resulting in a subsequent reduced structural material accumulation. This is undesirable since any deviation from a flat surface represents a deviation from the model used to design the air bearing topography, resulting in unexpected air bearing performance.
In addition to the shadowing effect, the structural element 6 typically comprises at least one region 10 where the structural material 4 accumulated excessively along the resist pattern boundary, resulting in a protuberant region oriented toward the disc surface termed a “fence”. This is undesirable since any deviation from a flat surface represents a deviation from the model used to design the air bearing topography. In addition, the fence is mechanically fragile and unstable so it tends to disintegrate during the disc drive operation.
In some existing lift off methods, multiple layers of protective, adhesive, and structural materials are deposed in succession, to avoid some of the shortcomings of the basic lift off method. In addition to the shadowing and fence effects, each of the multiple layers needed to construct the air bearing element adds uncertainty and error to the total height of the air bearing element, leading to unexpected air bearing performance.
The lift-off process produces undesirable side effects. In addition to an excessive number of process steps, many of the steps are potentially damaging to the air bearing structure. Of primary concern are the dimensional deviations from the desired dimensions of the applied structural material, caused by deposing the structural layer over the resist topology. The dimensional deviation results primarily from two sources: shadowing and fencing. Refer again to FIG. 1:
In the dimensional deviation caused by shadowing, the applied layer of structural material 6 does not possess a uniform thickness; since the relatively tall resist 3 areas shadow the areas near the patterned resist layer boundaries, e.g., Shadowed Region 5. This shadowing produces region 9, shown in FIG. 1 and again in FIG. 2 near the resist area boundaries that do not receive adequate structural material deposition flux to accumulate the needed thickness. The end result is a region, adjacent to the resist areas, where the applied structural layer 6 possesses inadequate height above the slider body; hence the structural element is not flat. It is also appreciated that this dimensional discrepancy is highly dependant on the photo resist layer thickness.
In the dimensional deviation caused by fencing, the applied layer of structural material 6 does not possess a uniform thickness. Some structural material deposition flux 7 deposits structural material along the sides and edges of the patterned resist boundaries. These deposits coat the resist boundary edges, illustrated by region 10, which are taller than the applied deposition of the structural element. When the resist is stripped away, exemplified in FIG. 2, the unwanted deposition of structural material 10 remains, forming a “fence” that extends above the thickness of the deposited element. Not only does this fence reduce the head-disc separation by an unpredictable amount, but the fence also lacks structural integrity and mechanical stability, so it tends to disintegrate during the disc drive operation. The fence may disintegrate into hard particulate matter, which is damaging and undesirable in the disc drive operation. In some instances, the head fabrication process may include an additional step, or sequence of steps, to remove the fence.
Further, the lift-off method requires an excessive number of manufacturing steps and processes, leading to increased costs and reduced production yields.
Further, the lift-off process will typically use a protective layer 2, which is needed to protect the slider body 1 from vigorous process steps (e.g., soda blast), corrosion and to enhance adhesion of subsequent layers. Presently used protective layers are too thick and opaque to permit measuring pole tip dimensions using the preferred method of critical dimension scanning electron microscopy (CDSEM). Furthermore, the protective layer requires two process steps to remove.